1. Field of the Invention
The invention relates in general to a dipole antenna, and more particularly to an ultra-wideband shorted dipole antenna that may be applied to a wireless communication band.
2. Description of the Related Art
Currently, the wireless communication frequency spectrum has been full with many application bands of the commercial wireless communication systems, such as the advanced mobile phone system (AMPS) ranging from 824 to 894 MHz, the global system for mobile communication (GSM) ranging from 880 to 960 MHz, the digital communication system (DCS) ranging from 1710 to 1880 MHz, the personal communication services (PCS) ranging from 1850 to 1990 MHz), the universal mobile telecommunication system (UMTS) ranging from 1920 to 2170 MHz and the worldwide interoperability for microwave access (WiMAX) ranging from 2500 to 2690 MHz, from 3400 to 3700 MHz and from 5250 to 5850 MHz. Thus, it is an inevitable trend to integrate various functions of commercial wireless communication application services in various traffic tools such as vehicles and buses with the better equipment. To achieve this object, the single traffic tool has to be equipped with multiple communication modules as well as multiple antenna systems. The multiple antenna systems require multiple coaxial signal cable lines, and the problems of the increased cost of manufacturing the antennas, the wasted space for accommodating the antennas and the electromagnetic interference have to be solved.
In view of the problems encountered in the multi-antenna systems, Taiwan Patent Publication No. TW574771 has disclosed a multi-meandered antenna with multiple bands and a single input to achieve the requirement of the multi-system wireless communication using the antenna having multiple resonance paths. However, the overall structure of the antenna becomes more complicated and the size thereof is significantly increased. U.S. Pat. No. 4,843,403 entitled “Broad-band Notch Antenna” has disclosed a broadband antenna structure similar to the dipole antenna. However, if the notch antenna has to be configured to operate in a lower band, the size of the antenna is also too large, the antenna cannot be properly attached to the vehicle window or hidden in a vehicle bumper, and the good impedance matching cannot be achieved in the resonance band. In addition, U.S. Pat. No. 6,975,281 entitled “Reduced Size Dielectric Loaded Spiral Antenna)” discloses a conventional ultra-wideband helical antenna having the reduced size by loading a multi-layer medium. However, the helical antenna has the complicated structure, the signal feeding portion needs an additional Balun to achieve the better impedance matching. The manufacturing cost of the antenna is increased due to the required Balun and the additionally loaded multi-layer medium.
Thus, it is an important subject in the industry to satisfy the requirement in the multi-system wireless communication and to overcome the bottleneck encountered when the above-mentioned antennas are actually applied.